Vehicles have become more and more automated to accommodate the desires of consumers. Vehicle parts, including windows, sun roofs, seats, sliding doors, and lift gates (e.g., rear latches and trunks) have been automated to enable users to press a button on the vehicle or on a remote control to automatically open, close, or otherwise move the vehicle parts.
When a vehicle closure system, such as a lift gate is elevated off the ground or from a closed position on a vehicle, some method is utilized to hold it up. As it is held above the ground or above a closed position of a vehicle, the mass of the lift gate under the influence of gravity equates to a substantial amount of weight and potential energy in the downward direction toward the closed position. When the closure system or lift gate is released from an open or held position, it travels downward to the closed position. Typically, sensors are employed to determine the actual position of the lift gate for determining the speed of the lift gate and whether it needs to be controlled or not in order to prevent the lift gate from slamming closed and possibly injuring the operator.
Several different types of sensors may be employed to determine the position and speed of a closing vehicle closure, such as Hall Effect sensors or optical vane interrupt sensors. One problem with the use of Hall Effect sensors or optical vane interrupt sensors is mechanical backlash due to system flex and unloaded drive mechanism conditions. As an example, when a lift gate is closing, the gate reaches a point where the weight of the lift gate begins to close the lift gate without any additional effort from the drive mechanism. In fact, at this point, the drive mechanism may apply effort to the lift gate to prevent premature closing. This is a state when negative energy is imparted from the drive mechanism to the lift gate.
The negative energy applied by the motor on the lift gate is used to control the downward velocity of the vehicle closure. For example, if a lift gate is closing too quickly, then a closed loop control algorithm instructs the controller to reduce the power applied to the motor or drive system until the desired velocity is achieved. Conversely, if the lift gate is closing too slowly, then the closed loop control algorithm instructs the controller to increase the power applied to the motor or drive system until the desired velocity is achieved. In either case, these conventional systems require additional power input into the motor to decrease or increase the closing speed of the vehicle closure.
Another problem associated with conventional lift gate closure systems is the substitution of conventional lift gate struts with power struts. Typically, conventional lift gate struts are simpler mechanical systems that require a smaller footprint or area for operation. As these are being replaced with motorized systems, such as motorized struts, the motorized struts are being designed to fit into the area or footprint typically occupied by the conventional struts. The desire to fit a motorized strut or system into the footprint or area of a conventional strut creates a size constraint for their gear train to be made as efficient as possible and their motor to be of a reduced size. Accordingly, these smaller gear trains and motors are less able to handle the forces of conventional closures apparatuses, such as lift gates, when the lift gates are accelerating closed due to gravity, thus causing the lift gates to slam closed.